Wafer-level fabrication of lidded chips with electrodeposited dielectric coating

ABSTRACT

A method is provided for fabricating a unit including a semiconductor element such as a sensor unit, e.g., for optical imaging. A semiconductor element has plurality of conductive features exposed at the front surface and semiconductive or conductive material exposed at at least one of the front and rear surfaces. At least some of the conductive features are insulated from the exposed semiconductive or conductive material. By electrodeposition, an insulative layer is formed to overlie the at least one of exposed semiconductive material or conductive material. Subsequently, a plurality of conductive contacts and a plurality of conductive traces are formed overlying the electrodeposited insulative layer, the conductive traces connecting the conductive features to the conductive contacts on the rear surface. The unit can be incorporated in a camera module having an optical element in registration with an imaging area of the semiconductor element.

RELATED APPLICATIONS

This application is a Continuation-In-Part of co-pending U.S.application Ser. No. 11/590,616, entitled Wafer-level Fabrication ofLidded Chips With Electrodeposited Dielectric Coating, filed on Oct. 31,2006, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to packaging of microelectronic devices,especially the packaging of semiconductor devices.

Certain types of microelectronic devices and semiconductor chips includedevices such as acoustic transducers, radio frequency emitters and/ordetectors and/or optoelectronic devices. Such devices typically requirepackaging which permits the passage of energy, e.g., acoustic, radiofrequency or optical wavelength energy to and from devices at a face ofa semiconductor chip.

Because such devices are often exposed at a front face of themicroelectronic devices, they usually require protection from theelements, such as dust, other particles, contaminants and/or humidity.For this reason, it is advantageous to assemble the microelectronicdevice with a lid or other element covering the front face of suchmicroelectronic device at an early stage of processing.

Other types of microelectronic devices require ease of testing. Thesegoals are furthered in some packaged semiconductor chips and modulesincorporating chips through use of a compliant pin-grid array orcompliant ball-grid array (“BGA”) external interface. Compliant pin-gridarray interfaces allow chips, especially for certain types of devicessuch as dynamic random access memories (“DRAMs”) to be temporarilyconnected to inexpensive fixtures for a variety of post-productiontesting, including burn-in tests and thermal stress tests. After suchtesting, the pin grid array interface allows the chip to be removed fromthe fixture and then installed more permanently in a final system.

For high speed performance, some types of chip packages incorporatecontrolled impedance transmission lines between contacts of thesemiconductor chips and the external contacts of the package. It isparticularly important to control the impedance seen by the wiring in apackage where distances between pads of the chip and the externalcontacts of the package are long.

Certain types of mass-produced chips such as DRAMs also requirepackaging costs to be tightly controlled. Processing used to packagesuch semiconductor chips can be performed on many chips simultaneouslywhile the chips remain attached to each other in form of a wafer orportion of a wafer. Such “wafer-level” processing typically is performedby a sequence of processes applied to an entire wafer, after which thewafer is diced into individual chips. Advantageously, wafer-levelpackaging processes produce packaged chips which have the same areadimensions as the original semiconductor chips, making theirinterconnection compact on circuit panels and the like.

Heretofore, wafer-level packaging processes have not been available forfabricating chips having pin-grid array interfaces or compliantball-grid array (“BGA”) interfaces which keep costs low while alsoincorporating controlled impedance transmission lines for high-speedperformance.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a method is provided offabricating a semiconductor element. In such method the semiconductorelement is provided which has a front surface, a rear surface remotefrom the front surface. At least one of conductive material orsemiconductive material being exposed at at least one of the front andrear surfaces and a plurality of first conductive contacts exposed atthe front surface, at least some of the first conductive contacts beinginsulated from the at least one of exposed semiconductive material orconductive material. An insulative layer is electrodeposited onto the atleast one of exposed semiconductive material or conductive material,forming (i) a plurality of rear conductive traces overlying the rearsurface, (ii) a plurality of front conductive traces overlying the frontsurface in conductive communication with the first conductive contactsand (iii) a plurality of edge conductive traces extending along edgesurfaces between the front and the rear conductive traces. The edgeconductive traces conductively connect the front conductive traces tothe rear conductive traces.

In accordance with another aspect of this invention the semiconductorelement includes a plurality of individual chips attached together atperipheral boundaries, the rear conductive traces are formed while thechips remain attached together and the edges are defined by removingmaterial of the semiconductor element in alignment with the peripheralboundaries.

In accordance with yet another aspect of this invention the frontsurface includes a conductive plane insulated from the first conductivecontacts and the insulative material is electrodeposited over theconductive plane.

In accordance with another aspect of this invention, the insulativelayer is simultaneously electrodeposited over semiconductive materialexposed at the rear surface when the insulative layer iselectrodeposited over the conductive plane.

In accordance with yet another aspect of this invention, the insulativelayer is electrodeposited over semiconductive material exposed at theedges.

In accordance with another aspect of this invention, the plurality ofchips are severed along the plurality of dicing lanes.

In accordance with one aspect of this invention, a semiconductor elementhas a front surface, first conductive contacts at the front surface, arear surface remote from the front surface and edges extending betweenthe front and rear surfaces. A polymeric coating overlies the frontsurface, the rear surface and the edges. A plurality of front conductivetraces are in conductive communication with the first conductivecontacts. The front conductive traces contact the polymeric coatingoverlying the front face. A plurality of rear conductive tracescontacting the polymeric coating overlying the rear surface. A pluralityof edge conductive traces contact the polymeric coating overlying theedges. The edge conductive traces connect the front conductive traces tothe rear conductive traces.

In accordance with another aspect of this invention, the semiconductorelement has a conductive plane at the front surface, and the polymericcoating contacts the conductive plane. At least portions of the firstconductive contacts are exposed within openings in the polymericcoating. In accordance with yet another aspect of this invention, firsttraces contact the polymeric coating. The first traces conductivelyconnect the first conductive contacts to the front conductive traces.

In accordance with yet another aspect of this invention, a dielectriclayer overlies the polymeric coating. The front conductive tracesconnect to the first conductive traces through openings in thedielectric layer.

In accordance with another aspect of this invention, the polymericinsulative layer includes an epoxy. In accordance with yet anotheraspect of this invention, the semiconductor element includes a pluralityof chips joined together at a plurality of dicing lanes.

In accordance with yet another aspect of this invention, thesemiconductor element includes a single chip.

In accordance with another aspect of this invention, bottom packagecontacts are conductively connected to the rear conductive traces.

In accordance with another aspect of this invention, a plurality ofmetallic bumps conductively connected to the plurality of rearconductive traces.

In accordance with yet another aspect of this invention, top packagecontacts are conductively connected to the front conductive traces.

In accordance with another aspect of this invention, a plurality ofmetallic bumps conductively connected to the plurality of frontconductive traces.

In accordance with yet another aspect of this invention, the pluralityof front conductive traces include a first metal layer having a firstthickness and a second metal layer having a second thicknesssubstantially greater than the first thickness.

In accordance with another aspect of this invention, the first metallayer includes at least one of aluminum or titanium, and the secondmetal layer includes nickel. In accordance with another aspect of thisinvention, a third metal layer overlies the second metal layer and thethird metal layer including copper.

In accordance with yet another aspect of this invention, the pluralityof rear conductive traces include a first metal layer having a firstthickness and a second metal layer having a second thicknesssubstantially greater than the first thickness.

In accordance with another aspect of this invention, the first metallayer includes at least one of aluminum or titanium, and the secondmetal layer includes nickel.

In accordance with yet another aspect of this invention, a third metallayer overlies the second metal layer, the third metal layer includingcopper.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view illustrating a packaged chip in accordancewith an embodiment of the invention.

FIG. 2 is a corresponding partial sectional view through portions of twopackaged chips which remain connected together along dicing lanes priorto being diced into individual units.

FIG. 3 is a perspective view facing a rear surface of a semiconductorelement or wafer, illustrating an intermediate stage in a method offabricating a packaged chip as illustrated in FIG. 1.

FIGS. 4A through 14 are sectional views illustrating stages infabrication of a packaged chip as illustrated in FIG. 1, according to anembodiment of the invention.

FIGS. 15A through 19B are plan views and corresponding sectional viewsillustrating stages in fabrication of a packaged chip in accordance withanother embodiment of the invention.

FIGS. 20A and 20B are a plan view and corresponding sectional viewillustrating a packaged chip in accordance with a variation of theembodiment of the invention illustrated in FIGS. 19A-19B.

FIG. 21A is a sectional view illustrating a packaged chip in accordancewith another embodiment of the invention.

FIG. 21B is a sectional view illustrating a packaged chip in accordancewith a variation of the embodiment of the invention illustrated in FIG.21A.

FIG. 22 is a schematic diagram illustrating a distribution ofcapacitance and inductance along wiring elements of a packaged chip.

FIG. 23 is a sectional view illustrating a packaged chip in accordancewith another embodiment of the invention in which each of a signalconductor and a reference conductor of a packaged chip follows a contourof an underlying exterior dielectric feature.

FIG. 24 is a sectional view illustrating a packaged chip in accordancewith a variation of the embodiment of the invention illustrated in FIG.23.

FIG. 25 is a sectional view illustrating a camera module in accordancewith one embodiment of the invention in which a sensor unit has bottomcontacts mounted to upwardly facing terminals on an upper surface of acircuit panel.

FIG. 26 is a sectional view illustrating a camera module in accordancewith another embodiment of the invention which includes a sensor unithaving a front face mounted to a lower surface of a circuit panel and anoptical unit having rear elements extending through a hole in thecircuit panel to abut or engage the sensor unit.

FIG. 27 is a perspective view illustrating a camera module in accordancewith a variation of the embodiment illustrated in FIG. 26, in which eachrear element extends through a separate hole in the circuit panel tocontact a sensor unit.

FIG. 28 is a sectional view illustrating a camera module in accordancewith another embodiment of the invention in which contacts on a frontface of the sensor unit are mounted to a lower surface of a circuitpanel and an optical unit has rear elements extending through a hole inthe circuit panel to abut or engage the sensor unit.

FIG. 29A is a sectional view illustrating a packaged chip in accordancewith another embodiment of the invention.

FIG. 29B is a top front view of a packaged chip in accordance with theembodiment illustrated in FIG. 29A.

FIG. 29C is a bottom rear view of a packaged chip in accordance with theembodiment illustrated in FIG. 29A.

FIGS. 30A through 30C and 30E are sectional views illustrating a stagein fabrication of a packaged chip in accordance with the embodimentillustrated in FIGS. 29A through 29C.

FIG. 30D is a partial perspective view facing a top surface of asemiconductor element or wafer, illustrating an intermediate stage in amethod of fabricating a packaged chip as illustrated in FIGS. 29Athrough 29C.

FIG. 31 is a perspective view of circuit panel and a stacked layer ofthe packaged chip in accordance with the embodiment illustrated in FIG.29A.

DETAILED DESCRIPTION

FIG. 1 is a sectional view of a packaged semiconductor chip 10 inaccordance with an embodiment of the invention. As illustrated in FIG.1, the packaged chip is shown in an orientation in which a front face102 of the semiconductor chip faces downwardly. As illustrated in FIG.1, the packaged chip includes a semiconductor chip 100 having a frontface 102 and a rear face 114 remote from the front face. The front faceof the chip 100 is covered by a lid or cover 104 which is assembledtogether with the semiconductor chip 100 to form the packaged chip 10.As illustrated in FIG. 1, the front face 102 of the semiconductor chip100 is oriented downwardly towards an upwardly facing inner surface 105of the lid 104. The semiconductor chip 100 typically includes asemiconductor substrate in which one or a plurality of semiconductordevices 112 are disposed in a device region thereof below the front face102. The semiconductor chip 100 also includes a plurality of dielectriclayers overlying the substrate, in which conductive metal wiring layersand vias (not shown) are disposed. The semiconductor devices 112 aredisposed at the front face of the chip and/or between the front and rearfaces of the chip.

The semiconductor chip 100 typically is connected to the lid 104 throughone or more standoff structures 124, which may include an adhesive, aninorganic or organic material and/or a joining metal. Structures forsupporting a lid at a constant spacing from a chip are described in thecommonly owned U.S. Provisional Application No. 60/761,171 filed on Jan.23, 2006, and U.S. Provisional Application No. 60/775,086 filed on Feb.21, 2006, the disclosures of which are hereby incorporated herein byreference. The packaged chip may include an interior cavity 106 betweenthe front face 102 of the chip and the inner surface 105 of the lid 104,as illustrated in FIG. 1. Alternatively, the packaged chip 10 can beconstructed without an interior cavity. When the cavity is present, thecavity's height 108 and the lateral dimensions, including lateraldimension 110, are typically determined, as for example, by the heightand dimensions of the structure 124 used to assemble the lid 104 withthe semiconductor chip 100. In a particular embodiment, the lid 104consists essentially of a glass or polymeric material and is at leastpartially transparent to electromagnetic spectra at frequencies ofinterest. The lid 104 may be only partially transparent to provide afilter function, or may be essentially transparent to a range offrequencies of interest.

The semiconductor devices 112 in the semiconductor chip 100 typicallyinclude electromagnetic transducer devices such as electromagnetic orelectro-optic devices which either detect or output electromagneticradiation. The semiconductor devices may be designed to emit or receiveradio frequency and/or optical wavelengths of infrared, visible and/orultraviolet or higher wavelength spectra including but not limited tox-ray wavelengths. Alternatively, the semiconductor devices 112 caninclude acoustic transducer devices, such devices being designed toconvert sound pressure waves received through a medium, e.g., air and/orother fluid medium (gas or liquid) to one or more electrical signals, orto convert one or more electrical signals into sound pressure waves.

In a particular embodiment, the packaged chip is a sensor unit in whichthe semiconductor devices 112 of the chip 100 include an imaging area107 for capturing an image. Electronic circuits (not shown) in chip 100are connected to the semiconductor devices in the imaging area 107 forgenerating one or more electrical signals representing an image capturedby the imaging area 107. Numerous electrical circuits are well known inthe imaging art for this purpose. For example, the semiconductor chip100 may be a generally conventional charge-coupled device (CCD) imagingchip with conventional circuits such as clocking and charge-to-voltageconversion circuits.

As seen in FIG. 1, the semiconductor chip includes a plurality of frontcontact pads 116 overlying an insulative or “passivation” layer 118 atthe front face of the semiconductor chip. The passivation layerpreferably includes an inorganic dielectric or organic dielectricmaterial. For example, the passivation layer 118 preferably includes adielectric material such as silicon dioxide, silicon nitride and/or acombination of materials such as a layered stack including silicondioxide and silicon nitride. While not specifically shown in FIG. 1, thesemiconductor devices 112 in the device region are conductivelyconnected to the front contact pads 116. The semiconductor device, thus,are accessible conductively through wiring incorporated within one ormore layers of the semiconductor chip 100 below and/or within thepassivation layer 118.

As further shown in FIG. 1, a second insulative layer 122 is disposedalong edges 120 of the semiconductor chip 100. The insulative layer 122preferably includes a conformally coated dielectric material. Theconformal coating covers at least portions of the edges 120 and rearsurface 114 of the chip. Preferably, the conformal coating covers theedges and rear face of the semiconductor chip continuously anduniformly, such that there are no breaks in the conformal coating andthe insulative layer 122 provides good dielectric isolation with respectto the semiconductor chip 100.

With further reference to FIG. 1, a plurality of conductive traces 126conductively connect the front contact pads 116 of the chip tocorresponding package contact pads 128 which overlie an exterior surfaceof the packaged chip 10. As specifically shown in FIG. 1, the packagecontact pads 128 overlie the rear surface 114 of the semiconductor chip100. The conductive traces 126 overlie the second insulative layer 122and extend over portions of the edges 120 and rear surface 114 of thesemiconductor chip. The conductive traces 126 preferably connectindividual front contact pads 116 of the chip 100 with correspondingindividual package contact pads 128 and conductive bumps 134.

As further shown in FIG. 1, a third insulative layer 130 overlies theconductive traces 126 and provides external isolation therefor. Thislayer can be referred to as an “external passivation layer” 130 of thepackage 10. In a particular embodiment, a metal structure 132 includinga metal layer or stack of metal layers including a wettable metal layeroverlies the package contact pads 128, and conductive bumps 134 overliethe metal structure 132. Typically, the conductive bumps 134 include afusible metal having a relatively low melting temperature such assolder, tin, or a eutectic mixture including a plurality of metals.Alternatively, the bumps 134 include a wettable metal, e.g., copper orother noble metal or non-noble metal having a melting temperature higherthan that of solder or other fusible metal. Such wettable metal can bejoined with a corresponding feature, e.g., a fusible metal feature of aninterconnect element such as a circuit panel to externally interconnectthe packaged chip 10 to such interconnect element. In anotheralternative, the bumps 134 include a conductive material interspersed ina medium, e.g., a conductive or solder-filled paste and/or an isotropicor anisotropic conductive adhesive.

The fabrication of packaged semiconductor chip 10 preferably isperformed simultaneously in quantity, i.e., by processing performedsimultaneously to a plurality of semiconductor chips while they remainjoined together as a portion of or an entire semiconductor device wafer.FIG. 2 is a partial sectional view through portions of two packagedchips 10. The packaged chips 10 include semiconductor chips 100 whichremain connected by a standoff structure 206 and a lid element or lidwafer 204 having dimensions corresponding to the semiconductor elementor wafer including chips 100. Preferably at a time after the fabricationof the insulative layers 118, 122, conductive traces 126, externalpassivation layer 130 and conductive bumps 134, the packaged chips 10are severed from each other along a dicing lane 208 of the lid element204 to form individual packaged chips 10, each packaged chip 10 being asillustrated in FIG. 1.

A method of simultaneously fabricating a plurality of packaged chips 10(FIG. 1) will now be described, with reference to FIGS. 3 through 14.With reference to FIG. 3, to summarize a feature of such method,portions of semiconductor material of a plurality of semiconductor chips100 which are registered with the front contact pads 116 of thesemiconductor chips are removed from a rear face 114 thereof. One ormore junction portions 300 of semiconductor material disposed betweenedges 120 of the semiconductor chips 100 are purposely allowed to remainafter this process. The presence of the one or more junction portions300 provides conductive continuity between exposed external edges of thesemiconductor chips 100 during the formation of an dielectric isolationcoating 122 (FIG. 1) overlying the edges 120 and rear faces 114 of thesemiconductor chips. In a preferred embodiment described below, thedielectric coating 122 is formed by electrodeposition, preferably byelectrophoretic deposition of a polymer.

Stages in fabrication of packaged chips 10 (FIG. 1) will now bedescribed with reference to FIGS. 4A through 14. FIG. 4A illustrates apreliminary stage of fabrication in which a plurality of standoffstructures 206 are formed extending outward from a major surface of alid element 204. Each standoff structure 206 typically has a rectangularshape aligned with dicing lanes 208 which lie at the boundaries betweenindividual lids to be severed from the original lid element 204. Asillustrated in FIG. 4B, the standoff structure 206 has a form which canbe described as that of a “picture frame ring shape.” As describedabove, the standoff structure can include one or more inorganic and/ororganic dielectric materials, semiconductors and/or conductors such asone or more metals. The standoff structure can be fabricated by additiveand/or subtractive processing, as described in, for example, U.S. patentapplication Ser. No. 10/949,674 filed Sep. 24, 2004, or U.S. ProvisionalApplication No. 60/761,171, the disclosures of which are herebyincorporated herein by reference. When the standoff structure includes ametal, it can be fabricated by a combination of steps includingsputtering of a thin layer of metal followed by subtractive patterningand then electroplating the remaining structure with a final metal.Alternatively, the standoff structure can be formed by electrolessplating, followed by subtractive patterning and electroplating.

In a particular embodiment, the standoff structure 206 is fabricated byelectrophoretic deposition of a polymer onto a preexisting sputtered orplated conductive layer, in a manner such as that described in theherein incorporated U.S. Provisional Application No. 60/775,086.

FIG. 5A illustrates a subsequent stage of fabrication after asemiconductor element 200 (a portion of or an entire semiconductordevice wafer) has been joined to a corresponding lid element. Prior tobeing joined with the lid element, a passivation layer 118 and thenfront contact pads 116 are formed, the front contact pads 116 beingexposed at the front surface of each semiconductor chip 100. The frontcontact pads 116 may be of a type commonly referred to as “compatiblepads.” Compatible pads are typically formed in such way as toconductively connect to other contacts, e.g., pads 212 of each chip 100which are farther away (in a lateral direction 210) from the dicinglanes, e.g., dicing lane 208. In one embodiment, the front contact pads116, e.g., the compatible pads, are not conductively connected to othercorresponding front contact pads across the intervening dicing lane 208.However, they can be so connected.

In the partial sectional view shown in FIG. 5A, portions of twosemiconductor chips 100 of a larger semiconductor element 200 are shownas attached through supporting structures 206 to corresponding portionsof a lid element 204 which includes lids 104. At this preliminary stage,semiconductor chips 100 are joined together at boundaries such as theboundary defined by dicing lane 208.

In a subsequent stage of fabrication illustrated in FIG. 5B, thesemiconductor element 200 is shown inverted in relation to the viewshown in FIG. 5A. As shown in FIG. 5B, a thickness of the semiconductorelement 200 has been reduced, as by grinding and/or lapping from a rearface 114 thereof. Reducing the thickness of the semiconductor element200 can assist in achieving a final packaged chip having a desirablysmall thickness 214. The lid element 104 overlying the front face of thesemiconductor chip assists in providing structural support to thesemiconductor chip, increasing its rigidity to permit the thickness ofthe packaged chip to be reduced as desirable to a smaller thickness.

Thereafter, a subsequent stage of fabrication is shown in FIG. 6 inwhich an opening 216 is formed the semiconductor element 200 inregistration with the dicing lane 208 between adjacent semiconductorchips 100. Openings preferably are formed which extend along the lengthof each edge 120 of each semiconductor chip as viewed in FIG. 3.Openings like the opening 216 shown in FIG. 6 preferably are formed bydepositing a photoimageable layer 218, e.g., a photoresist,antireflective coating or other layer, patterning openings in thephotoimageable layer by photolithography and then etching thesemiconductor element from the rear face 114 in accordance the openingstherein. The edges 120 of each chip 100 which are exposed at the wallsof the openings preferably are oriented preferably at an angle 248 ofbetween about 10 and 60 degrees from a normal 246 to the front face ofthe semiconductor chip. Preferably, the semiconductor element is etchedisotropically using an etchant which attacks the semiconductor material,e.g. silicon, of the semiconductor element but which does not attack amaterial included in the passivation layer 118. In this way, thepassivation layer functions as an etch stop protecting the front contactpads 116 when openings in the semiconductor element 200 are etched.

Referring to FIG. 7, after the openings are formed in the semiconductorelement, the patterned photoimageable layer is removed from theassembly. At that time, the assembly appears as shown in FIG. 3, havingsemiconductor material portions removed where they overlie the frontcontact pads 116. For ease of illustration, the passivation layeroverlying the contact pads 116 is not shown in FIG. 3. The assemblyincluding the semiconductor element with the lid element attachedthereto is then immersed in a dielectric deposition bath. The assemblyis then held there under appropriate conditions for a sufficient time toform an electrodeposited conformal dielectric coating 220 on exposedexterior conductive and/or semiconductive surfaces of the semiconductorelement. Preferably, an electrophoretic deposition technique is utilizedto form the conformal dielectric coating, such that the conformaldielectric coating is only deposited onto the exposed conductive and/orsemiconductive surfaces of the assembly. The electrophoreticallydeposited coating is self-limiting in that after it reaches a certainthickness governed by parameters, e.g., voltage, concentration, etc. ofits deposition, deposition stops. Electrophoretic deposition forms acontinuous and uniformly thick conformal coating where on conductiveand/or semiconductive exterior surfaces of the assembly. In addition,the electrophoretically deposited coating preferably does not form onthe passivation layer 118, due to its dielectric (nonconductive)property.

Preferably, the conformal coating is formed from a cathodic epoxydeposition precursor. Alternatively, a polyurethane or acrylicdeposition precursor could be used. A variety of electrophoretic coatingprecursor compositions and sources of supply are listed in Table 1below.

TABLE 1 ECOAT NAME POWERCRON 645 POWERCRON 648 CATHOGUARD 325MANUFACTURERS MFG PPG PPG BASF TYPE CATHODIC CATHODIC CATHODIC POLYMERBASE EPOXY EPOXY EPOXY LOCATION Pittsburgh, PA Pittsburgh, PASouthfield, MI APPLICATION DATA Pb/Pf-free Pb-free Pb or Pf-free Pb-freeHAPs, g/L 60-84 COMPLIANT VOC, g/L (MINUS WATER) 60-84 <95 CURE 20min/175 C. 20 min/175 C. FILM PROPERTIES COLOR Black Black BlackTHICKNESS, μm 10-35 10-38 13-36 PENCIL HARDNESS 2H+ 4H ECOAT NAMEPOWERCRON 645 POWERCRON 648 CATHOGUARD 325 BATH CHARACTERISTICS SOLIDS,% wt. 20 (18-22) 20 (19-21) 17.0-21.0 pH (25 C.) 5.9 (5.8-6.2) 5.8(5.6-5.9) 5.4-6.0 CONDUCTIVITY (25 C.) μS 1000-1500 1200-1500 1000-1700P/B RATIO 0.12-0.14 0.12-0.16 0.15-0.20 OPERATION TEMP., C. 30-34 3429-35 TIME, sec 120-180 60-180 120+ ANODE SS316 SS316 SS316 VOLTS200-400 >100 ECOAT NAME ELECTROLAC LECTRASEAL DV494 LECTROBASE 101MANUFACTURERS MFG MACDERMID LVH COATINGS LVH COATINGS TYPE CATHODICANODIC CATHODIC POLYMER BASE POLYURETHANE URETHANE URETHANE LOCATIONWaterbury, CT Birmingham, UK Birmingham, UK APPLICATION DATA Pb/Pf-freePb-free Pb-free HAPs, g/L VOC, g/L (MINUS WATER) CURE 20 min/149 C. 20min/175 C. 20 min/175 C. FILM PROPERTIES COLOR Clear (+dyed) Black BlackTHICKNESS, μm 10-35 10-35 PENCIL HARDNESS 4H BATH CHARACTERISTICSSOLIDS, % wt. 7.0 (6.5-8.0) 10-12 9-11 pH (25 C.) 5.5-5.9 7-9 4.3CONDUCTIVITY (25 C.) μS 450-600 500-800 400-800 P/B RATIO OPERATIONTEMP., C. 27-32 23-28 23-28 TIME, sec 60-120 ANODE SS316 316SS 316SSVOLTS 40, max 50-150

After electrophoretically depositing the conformal dielectric coating,processing is then begun for forming conductive traces which connect thefront contact pads of the semiconductor chips to exterior contacts ofthe packaged chips. As illustrated in FIG. 8, portions of the dielectricpassivation layer 118 extending beyond the conformal dielectric coating220 at edges 120 of the semiconductor chips is now removed. Removal ofthe passivation layer can be performed, for example, through use of anetchant which attacks the passivation layer 118 while not substantiallyattacking the conductive material, e.g., one or more metals which areincluded in the front contact pads. An exemplary process for etching thepassivation layer includes plasma etching performed in a manner whichselectively does not attack organic materials so as to preserve theexposed conformal dielectric coating 220. Following the removal of thepassivation layer overlying the front contact pads, optionally a grooveis cut between the standoff structures on each side of the dicing lane,such as through use of a saw designed to make a “V”-shaped grooveseveral microns in width. This process exposes conductive edges of thefront contact pads along walls of the V-shaped groove.

Thereafter, as illustrated in FIG. 9, a metal layer 222 for formingconductive traces is deposited to overlie the conformal dielectriccoating 220. The metal layer preferably is deposited by sputtering aprimary metal layer onto exposed surfaces of the assembly, or byelectroless deposition. In one embodiment, the primary metal layerincludes or consists essentially of aluminum. In another particularembodiment, the primary metal layer includes or consists essentially ofcopper. In yet another embodiment, the primary metal layer includes orconsists essentially of titanium. One or more other exemplary metals canbe used in a process to form the primary metal layer.

Subsequently, with reference to FIG. 10, a photoimageable layer isdeposited to overlie the primary metal layer and a three-dimensionalphotolithographic patterning process is utilized to pattern the primarymetal layer, such as the process described in U.S. Pat. No. 5,716,759 toBadehi, the disclosure of which is hereby incorporated by referenceherein. Thereafter, remaining portions of the photoimageable layer areremoved. As a result, individual conductive patterns are formed whichcorrespond to the dimensions of conductive traces to be formed thereon.Following patterning of the primary metal layer into individual lines,the photoimageable layer is removed from the semiconductor element andan electroplating process is used to plate a secondary metal layer ontothe primary metal layer to form individual conductive traces 226extending from the front contact pads 116 along edges 120 and onto therear faces 114 of the semiconductor chips. The secondary metal mayinclude nickel or other noble metal. In one embodiment, theelectroplated second metal on the primary metal layer completes theconductive traces. Alternatively, an optional third metal layer such asgold, platinum or palladium may be plated onto the secondary metal forproviding corrosion resistance to complete the conductive traces. Duringthe electroplating process, a plug 224 including the second metal layerand optional third metal layer forms overlying exposed surfaces of thefront contact pads 116 and which may line or fill the gap betweenadjacent standoff structures 206.

Subsequently, as illustrated in FIGS. 11-14, further processing isperformed to define package contacts overlying the rear face 114 of thesemiconductor chips. As illustrated in FIG. 11, an additionalphotoimageable layer 230 is deposited and patterned to cover portions ofthe conductive traces 226 where wettable metal contacts and preferablyconductive bumps are to be formed.

Referring to FIG. 12, a further process is performed to passivateexterior surfaces of the packaged chips. Preferably, a furtherelectrophoretic process is employed to form a third insulative layerincluding uniformly thick conformal dielectric coating 232 overlyingeach of the conductive traces 226 on the rear surface 114 and edges 120.During that process, the metal plugs 224 provide conductive continuitybetween semiconductor chips 100 of the semiconductor element.Thereafter, the photoimageable layer 230 is removed by selective removalprocess, such as dissolution in a solvent or selective etching. FIG. 12illustrates a particular stage in processing after the externalconformal dielectric coating 232 has been formed and the patternedphotoimageable layer has been subsequently removed, leaving openings 228in the external passivating layer 232.

Alternatively, instead of depositing the conformal dielectric coating232 by electrophoretic deposition as described with reference to FIGS.11 and 12, the conformal dielectric coating 232 can be formed byspin-coating and/or spray coating a photoimageable dielectric such as anencapsulant towards the rear face and edges 120 of the semiconductorchip to form a relatively uniformly thick coating. Thereafter, openings228 are formed in the conformal dielectric coating 232 byphotolithographic process. One or more processes, e.g., heating etc. maybe performed to cause the conformal dielectric coating 232 to hardenafter the initial deposition of the photoimageable material.

Subsequently, as illustrated in FIG. 13, conductive structures 236including a wettable metal layer are formed within the openings of thepassivating layer 232. For example, wettable metal features 236 of thetype commonly referred to as “under bump metallization” (“UBM”) areformed within the openings to overlie the conductive traces 226.

Thereafter, as further illustrated in FIG. 13, conductive bumps 234 arejoined to the wettable metal features 236. As described above withreference to FIG. 1, the conductive bumps can include one or moreconductive materials. For example, the conductive bumps can include afusible metal such as solder, tin, or a eutectic composition and/or oneor more noble metals, for example, copper, nickel, etc. In a preferredembodiment, the conductive bumps are formed by placing spheres includinga fusible metal such as solder, tin or eutectic onto the wettable metalfeatures 236 and then heating the conductive bumps thereto to fuse themto the wettable metal features 236.

Finally, the packaged chips are severed from each other along dicinglane 208 by sawing or other dicing method to form individual packagedchips as illustrated in FIG. 14. A variety of exemplary processes forsevering packaged chips into individual units are described in theherein incorporated commonly owned U.S. Provisional Application Nos.60/761,171 and 60/775,086, any of which can be used to sever thepackaged chips to form individual packaged chips as shown in FIG. 14.During the process used to sever the assembly into individual packagedchips 10 (FIG. 14), metal features 224 disposed between the frontcontact pads preferably are removed, such that individual ones of thefront contact pads 116 on the semiconductor chips are conductivelydisconnected from each other.

Referring now to FIGS. 19A-19B, in a microelectronic structure 350according to another embodiment of the invention, conductive features310 at a front face 302 of a semiconductor chip 300 are covered with adielectric material 304 by an electrophoretic deposition process. Theelectrophoretically deposited dielectric coating 304 serves as adielectric level on which conductive traces 306 and additionalconductive contacts 308 can be disposed above the front face 302 of thechip. As the traces 306 and additional contacts 308 are in conductivecommunication with original contacts 310 of the chip, the conductivetraces 306 and additional conductive contacts 308 serve to redistributethe conductive contacts from the original contacts 310 of the chip.

In the microelectronic structure 350 illustrated in FIGS. 19A-19B, theconductive trace 306 has an advantageous microstrip line relationshipwith the conductive feature 316 on which the electrophoretic coating 304is formed. In a microstrip line, a uniformly thick dielectric layerseparates a signal-carrying conductor from another conductor, e.g.,ground plane which is held at a reference potential such as ground orother typically fixed potential. In one example, the signal-carryingconductor includes trace 306 and contact pad 308, and the otherconductor 316 at the front face 302 of the chip is held at fixedpotential such as ground. Openings 325 in the electrophoretic coating304 can be provided selectively, such that only certain contacts 310 ofthe chip are connected to conductive traces 306 and conductive pads 308of the chip for redistribution. Other contacts of the chip can beconnected to the ground plane or reference conductor 316 at the frontface of the chip.

A method of fabricating the microelectronic structure illustrated inFIGS. 19A-19B will now be described with reference to FIGS. 15A through18B. FIGS. 15A and 15B illustrate a preliminary stage in the formationof the microelectronic structure 350. As shown therein, a plurality ofexposed conductive contacts 310 are provided at the front face 302 of amicroelectronic chip such as a semiconductor chip having active devicestherein. A dielectric layer is provided in areas of the front face otherthan where the conductive contacts are exposed, such dielectric layerusually being referred to as a “passivation layer.” The conductivecontacts 310 of the chip are shown arranged in a row. However, thecontacts 310 need not be arranged in one line. The contacts 310 can bedisposed at or near peripheral edges 314 of the chip or the contacts 310can be disposed at locations farther away, or even well removed from theedges 314.

Preferably, the processing described herein for fabricating thestructure shown in FIGS. 19A-19B is performed simultaneously to aplurality of chips while the chips remain attached together in form of awafer or portion of a wafer. As illustrated in FIGS. 16A and 16B, in astep prior to forming the electrophoretic coating, a masking layer 312is formed in registration with at least some of the contacts 310 toprevent the electrophoretic coating from being formed thereon.Preferably, an inorganic dielectric material such as an oxide of siliconhaving a thickness of 10 μm (microns) or greater is blanket-deposited tooverlie the front face 302 of the chip. Thereafter, the layer ofinorganic dielectric material is removed in areas except where theinorganic dielectric material overlies certain ones of the contacts 310.In this way, the inorganic dielectric layer remains as a masking layerover some, but not all of the contacts 310. For example, as shown inFIG. 16A, a particular contact 315 remains uncovered by the maskinglayer 312.

In a subsequent stage of fabrication illustrated in FIGS. 17A and 17B, ametal layer 316 is blanket deposited to overlie the front face 302 ofthe chip. Thereafter, the masking layer 312 (FIGS. 16A-16B) is removedfrom the contacts 310, leaving the previously masked contacts exposedonce again. However, the blanket deposited metal layer is formed inconductive communication with the particular contact 315 that was notmasked by masking layer 312. As will be described below, the blanketmetal layer 316 is typically used for the purpose of a ground plane.Therefore, the particular contact 315 will be conductively connected tothe blanket deposited metal layer when other contacts 310 are exposedafter removal of the masking layer 312.

Thereafter, with reference to FIGS. 18A-18B, an electrophoreticdeposition process is utilized to apply a dielectric coating 304 on themetal layer 316. The dielectric coating 304 has a thickness of betweenabout one μm (micron) and 100 μm, and preferably between about one μmand 15 μm. The dielectric layer 304 has a substantially flat top surface320 and typically has a gradual, sloping transition 305 between thefront face 302 of the chip 300 and the top surface 320. This transition305 may follow a line of curvature from the substantially flat topsurface 320 or may simply be canted at an angle such that the transition305 is not too vertically oriented in relation to the front face 302 andthe top surface 320.

The electrophoretically deposited layer 304 preferably includes a lowmodulus of elasticity material, such as may be obtained byelectrophoretic deposition of polymeric materials such as flexibilizedepoxy, silicones, acrylics, etc. Alternatively, a flexibleelectrophoretic coating, capable of buckling or wrinkling to accommodaterelative movement, can be fabricated from high elastic modulusmaterials, normally considered as “rigid,” provided that these materialsare present in thin layers. Relatively soft materials can be used ingreater thicknesses and provide a highly flexible coating. Such softmaterials provide a highly compliant interposer or underlayer for theplacement of conductive contacts thereon, i.e., an interposer which isreadily compressible in the directions perpendicular its surfaces andwhich, therefore, permits movement of the terminals in these directions.

An advantage of forming the dielectric coating by electrophoreticdeposition is that deposition occurs in response to application of anelectric field. Accordingly, conditions are most favorable fordeposition in areas where a conductor is exposed and is held at acertain potential in relation to the fluid deposition medium. In otherareas where no exposed conductor is present and where the electric fieldis much weaker, deposition is minimal or non-existent. For this reason,the electrophoretic coating does not form on conductors which are notconductively connected to the required source of electric potential,even when such conductors are exposed directly to the deposition medium.In this way, contact pads 310 which are not conductively connected tothe metal layer 316 remain free or substantially free of the depositedcoating after the electrophoretic deposition process.

One characteristic of electrophoretic deposition is that the thicknessof the resulting dielectric layer varies in relation to the strength ofthe electric field. For this reason, as illustrated in FIGS. 18A and18B, the thickness 322 of the electrophoretically deposited dielectriclayer 304 generally is constant over interior portions 320 of aconductive planar surface such as the ground plane 316. On the otherhand, the thickness of the electrophoretically deposited dielectriclayer 304 decreases gradually from its nominal thickness 322 to zero atboundaries of the conductive surface, i.e., at edges of the conductivesurface. The resulting dielectric layer has a sloped edge, rather thanan abrupt edge.

As shown in FIG. 18B, typically, the electrophoretic dielectric coating304 extends somewhat beyond the edges 324 of the conductive surface. Inthis way, the dielectric coating 304 overlies portions 326 of the frontface 302 of the chip adjacent to edges 324, but tapers off to zerothickness to leave contacts 310 exposed.

Thereafter, in the subsequent stage of fabrication shown in FIGS.19A-19B, conductive traces 306 are formed which extend along the topsurface of the dielectric and down the sloped edges to conductivelyconnect to the original conductive contacts 310 of the chip 300. Thesloping edges of the dielectric layer 334 enable conductive traces 306to be provided which are subject to substantially less fatigue fromthermal and mechanical stresses than would be the case if the edges ofthe dielectric layer 304 were at right angles to its top and bottomsurfaces.

Simultaneously, outer conductive contacts 308, e.g., lands, are formedtogether with the conductive traces 306 in locations overlying anexposed surface of the dielectric coating 304. The fabrication of theseadditional lands 308 and traces 306 can be performed by processing asdescribed above with reference to FIGS. 9 through 12. Further processingsimilar to that described with reference to FIGS. 13-14 above can beperformed to fabricate ball grid array (“BGA”) contacts and to severindividual chips from a larger assembly, e.g., semiconductor wafer orportion of semiconductor wafer. In a particular embodiment, a soldermask or other type of external passivation layer 321 can be formed,electrically isolating the original chip contacts 310, while leaving thecontacts 308 exposed as lands or bond pads for the interconnection ofbond wires thereto.

FIGS. 20A-20B illustrate a variation of the embodiment shown anddescribed with reference to FIGS. 19A-19B above. As illustrated therein,a plurality of post-like or pin-like contacts 318 project upwardly fromcontact pads 308 overlying the electrophoretically deposited dielectriclayer. Preferably, the contacts 318 are solid metal features and havefrustum, conical or pyramidal shape. In one embodiment, the contacts 318extend to a height 335 of about 100 μm above the surface of the contactpad 308, have a diameter at a base surface of about 200 μm, and have adiameter at a top surface or “tip” of about 50 μm.

Preferably, the contacts consist essentially of a metal such as copperor other metal which has a melting temperature higher than that of afusible metal, e.g., solder. In that way, contacts 318 remain solidduring processes used to bond the contacts 318 of the chip to othermicroelectronic structures as a chip carrier, interposer, circuit panelor the like. In one example, the contacts 318 can be fabricated throughan additive process such as electroplating, or via transfer from anadhesively backed article and metallurgical bonding the contacts 318 tothe contact pads. Alternatively, the contacts 318 can be fabricated viasubtractive processing such as etching from a metal layer in accordancewith a mask pattern. As further shown in FIGS. 20A-20B, an additionaldielectric layer 321 overlies the surface of the conductive traces 306and contact pads 308 as an external passivation layer or solder mask.

In the embodiment of the invention illustrated in FIGS. 20A-20B, thethickness of the electrophoretically deposited dielectric layer 304 isconstrained by the thermal-mechanical properties of the semiconductorwafer, e.g., silicon wafer and those of the dielectric layer. Even whenthe modulus of the dielectric layer 304 is quite low, the product of thethickness, the modulus and the mismatch between the thermal expansioncoefficients of the two materials can cause the wafer to warp or bowunder a relatively large change in temperature when the thickness of thedielectric layer is sufficient. Any warping of the semiconductor waferis problematic because equipment and facilities are designed to processsemiconductor wafers which are planar or have nearly perfect planarity.In addition, thermal expansion mismatch may cause the contacts 308thereon to expand or shrink out of alignment with contacts of anexternal microelectronic element with which they mate. FIG. 21Aillustrates a further variation of the above-described embodiment of theinvention in which the thickness of the dielectric layer is made greaterin locations where the dielectric is disposed between the conductiveplane and individual external contact pads 308. Increasing the thicknessof the dielectric layer in such locations allows the external contactpads 308 to be placed at greater height above front surface whilekeeping stresses due to thermal expansion mismatch at a manageablemagnitude.

In this embodiment, the dielectric layer includes an initial dielectriclayer 304 which is electrophoretically deposited as described above.After forming that layer 304, a region 334 of additional compatibledielectric material is formed in specific locations overlying thedielectric layer 304. In such way, dielectric region 334 and dielectriclayer 304 together form a combined region of dielectric material betweenthe contact pad 308 and the conductive plane 316, the combined regionhaving a thickness 330 from the conductive plane 316 which is greaterthan that of the original dielectric layer.

In an alternative embodiment, the additional region 334 includes adifferent material than that of the electrophoretically depositeddielectric layer 304. Preferably, the additional region 334 has a lowermodulus than that of the electrophoretic dielectric layer 304. In thisway, the increased thickness of the combination of the additional regionwith the electrophoretic dielectric layer 304 provide a higher degree ofcompliancy than either layer provides by itself. As an example of use,one or both of the dielectric layer 304 and the additional region 334are relatively compliant, i.e., have relatively low modulus andsufficient thickness. In such case, when a contact 318 overlying theadditional region 334 is brought into mating contact with a terminal ofan external element (not shown), the compliant material below the baseof the contact 318 can flex. This permits the tip of the contact 318 toremain in mating contact with the terminal of the external element evenwhen the mating surfaces of contacts and the external terminals are notperfectly planar.

FIG. 21B is a sectional view illustrating a microelectronic structure inaccordance with a variation of the embodiment depicted in FIG. 21A. Inthis case, the contact includes a bump 340 including a fusible metalsuch as solder, tin or eutectic composition, instead of a post-likeprotrusion 318 (FIG. 21A). Alternatively, the bump 340 can include asolid or hollow core and a coating of such fusible material, the corecontaining one or more other materials such as copper or a polymer.Preferably, the bump 340 is arranged as one of many bumps overlyingsimilar raised regions 334 of dielectric material in an arrangementreferred to as a “ball grid array” (BGA).

FIG. 22 is a diagram of a network which models the electrical impedancecharacteristics of the structure illustrated in FIG. 21A. As illustratedin FIG. 21A, inductance and capacitance in the network is distributed,as modeled by inductors 360 and capacitors 362, which occur asparallel-disposed impedance elements in the network. To achieve goodtransmission of signals, capacitance and inductance are constantthroughout the network.

The inductance and capacitance seen by each of the conductive traces 346shown in FIGS. 21A-B varies with position along their lengths. Thevalues of these parameters depend on the type of dielectric material inthe dielectric regions 334, 304, as well as the thickness of thedielectric material from conductive plane 316 and the width of theconductive traces. The dielectric characteristics of regions 304, 334are constant with position along the length of each trace. The width ofeach trace is also constant. For a variety of reasons, it is impracticalfor the widths of the traces 346 to vary between the original contacts310 of the chip and the outer contacts 308. As a result, the increasedthickness of the dielectric material directly underlying the contacts318 causes the inductance and capacitance seen by the traces to varyalong their length. Variations in impedance of this sort areproblematic. Decreased tuning of the circuit and losses due to signalreflection can result.

In a further variation of the above-described embodiment illustrated inFIG. 23, the aforementioned problems due to the non-uniform thickness ofthe dielectric layer 336 are addressed. Here, the surface of the lowerconductor 336 is arranged such that it remains parallel to the externalconductive traces 346 at a constant or near constant spacing thereto. Inthis case, a flat portion 356 of the lower conductor extends a distancealong the front face of the chip. Then the lower conductor jogs upwardalong a wall portion 337 adjacent to a dielectric region 344. The wallportion 337 preferably is sloped such that the flat portion 356 is notat a right angle with the wall portion 337. Rather, the flat portionmakes a gradual transition with the wall portion. An upper flat portion366 also makes a gradual transition with the wall portion 337 at alocation overlying dielectric region 344.

Fabrication of the microelectronic structure illustrated in FIG. 23 issimilar to that of the structure shown in FIG. 21A. However, in thiscase, an additional dielectric region 344 is formed prior to forming thelower conductor and then forming the electrophoretically depositeddielectric coating 368 overlying the lower conductor 336. Thesubstantially uniform thickness 362 of the dielectric coating 368results from the electrophoretic deposition technique used to form thedielectric coating thereon. As mentioned above, electrophoreticdeposition has a self-limiting quality such that its thickness isrelated to the strength of the electric field. Therefore, theelectrophoretically deposited coating takes on the profile of theconductor which underlies the coating. For this reason, the conductivetraces 346 of the resulting structure, shown in FIG. 23, remain atconstant spacing to the lower conductor 336, to provide a transmissionline having constant impedance.

FIG. 24 illustrates a variation of the structure illustrated in FIG. 23,in which a conductive bump 370, rather than a post-like contact, isprovided for externally connecting the chip to terminals of an externalmicroelectronic element.

A camera module 1030 according to an embodiment of the invention (FIG.25) includes a sensor unit 1020 having contacts 1042 disposed on therear face of the sensor unit, i.e., on the surface of the semiconductorchip 1000 opposite from the front surface 1028 which carries the imagingarea 1026. The sensor unit can be such as that shown and described abovewith reference to FIG. 1. Similar sensor units and camera modules aredescribed in commonly owned U.S. patent application Ser. No. 11/265,727filed Nov. 2, 2005 and Ser. No. 11/322,617 filed Dec. 30, 2005, thedisclosures of which are hereby incorporated herein by reference. Thecontacts 1042 of the sensor unit are connected to terminals 1080 of acircuit panel 1070 by masses 1082 of fusible conductive material such assolder.

The optical unit 1050 in this arrangement includes a turret or supportstructure 1051 having a mounting portion 1052 arranged to hold one ormore lenses or other optical elements 1058. The support structure 1051also includes a plurality of rear elements 1062 in the form of elongatedposts 1062 projecting rearward from the mounting portion 1052. Theseposts have rear surfaces 1054 which abut or mechanically engage areference plane in the sensor unit to position the optical unit relativeto the sensor unit. In the example illustrated in FIG. 25, the rearsurfaces 1054 abut the front surface of the transparent cover 1034 whichoverlies the imaging area 1026. Alternatively, the turret or supportstructure includes registration features, e.g., posts, pins, recesses,or the like, for mechanically setting the height of the optical unit1050 with respect to the chip 1000, while limiting tilt of the turretwith respect to the imaging area 1026 of the chip.

It is desirable to make the connection between the rear surfaces of theposts 1062 and the front surface 1034 level and uniform in thickness. Inanother way to achieve this purpose, metallic attachment features orpads 1055 can be provided at the outer surface 1036 of the cover 1034,which are metallurgically bonded, e.g., via diffusion bonding, tometallic features at the rear surfaces 1054 of the posts 1062.Alternatively, a somewhat thin adhesive can be used to bond the rearsurfaces of the posts to the cover.

In another embodiment, in place of posts, the turret or supportstructure 1051 includes a rear element which encloses or substantiallyencloses a volume having a cylindrical or polyhedral shape. Such rearelement can be provided which has a cylindrical wall or polyhedralshaped (e.g., box-shaped) wall, in which the rear surface of the rearelement abuts against a reference plane of the sensor unit such asprovided at the outer surface 1036 of the cover 1034.

In a variation of the above embodiment shown in FIG. 26, sensor unit1020 is mounted with the front of the sensor unit, and hence, imagingarea 1028 facing forwardly, toward the rear or bottom surface of circuitpanel 1070. The contacts 1042 of the sensor unit are connected bysuitable leads or wire bonds 1002 to the conductors 1076 of the circuitpanel. In this embodiment, the rear elements 1062 of the optical unit1050 project through a hole 1072 in the circuit panel aligned with theimaging area 1028. Stated another way, hole 1072 is large enough toaccommodate the light path from the optical element to the imaging areaand also accommodate the rear elements 1062. A similar arrangement canbe used with sensor units having contacts on the front face, asdiscussed above.

A camera module in accordance with a further embodiment of the invention(FIG. 27) includes a sensor unit 920, depicted in broken lines, disposedon the bottom or rear side of a circuit panel 970. Here again, theimaging area of the chip in the sensor unit is aligned with a hole 972in the circuit panel. The optical unit 950 in this arrangement includesa turret or support structure 952 having a mounting portion 902 arrangedto hold one or more lenses or other optical elements 958. The supportstructure 952 also includes a plurality of rear elements 962 in the formof elongated posts projecting rearward from the mounting portion 902.These posts extend through apertures 974 in the circuit panel, and thusmechanically engage the sensor unit to position the optical unitrelative to the sensor unit as discussed above. Here again, posts definegaps between them as, for example, gap 963 a between posts 962 a and 962b. Here again, the circuit panel 970 may extend into the gaps, and hencemay extend between the sensor unit and optical unit, which facilitatesmaking connections to the sensor unit as discussed above. In theembodiment of FIG. 27, the gaps have substantial height. The heightH_(G) of the gap in the completed assembly is equal to the height of themounting element 902 above the front surface 901 of circuit panel 970.The height H_(G) desirably is on the order of 2 mm or more, moredesirably 5 mm or more, and most preferably 1 cm or more. The width ofeach gap (i.e., the horizontal distance, parallel to the circuit panel,between rear elements 962 a and 962 b) desirably also is at least about2 mm, more desirably at least about 5 mm, and most desirably at leastabout 1 cm. As further discussed below, provision of such large gapsallows access into the area between the optical element and hole 972 forperforming operations on the completed assembly. The large gaps,however, can be provided without increasing the overall height of theassembly. The distance between the optical elements such as lens 958 andthe sensor unit is set by the optical properties of the system as, forexample, the focal length of lens 958. Therefore, the lens must besupported at a substantial distance forward of the circuit panel in anyevent.

A module or assembly in accordance with the embodiment of FIG. 27 can betreated after assembly by performing operations on the sensor unitthrough the gap or gaps, and desirably also through hole 972 in thecircuit panel. For example, the assembly may be subjected to a cleaningoperation in which a cleaning fluid, a cleaning implement, or both areinserted into one or more of the gaps and through hole 972 to clean thesurface of the sensor module. For example, where the sensor moduleincorporates a cover facing forwardly toward the rear or bottom surfaceof the circuit panel, the area of the cover aligned with the hole whichincludes the area aligned with the imaging area of the sensor chip canbe cleaned. The ability to perform such a cleaning operation on thecompleted assembly counteracts the effects of contamination during theassembly process. This, in turn, can provide a higher quality cameraunit, and also can allow some relaxation of the conditions appliedduring assembly to provide contamination. For example, a “clean room”environment may be unnecessary, or alternatively, a less expensive,lower-quality clean room may be used. In a further example, the sensorunit may not incorporate a separate cover, but instead may consist onlyof a “bare” semiconductor chip having an imaging area and having apassivation layer in the form of a thin coating effective to protect theelements of the bare chip from chemical or mechanical damage during theassembly process. Such a bare imaging chip typically requires verystringent precautions during handling to avoid deposition of dirtoverlying one or more imaging elements. The requirements are somewhatless stringent for sensor units which incorporate a cover. However, bypost-cleaning after assembly, the less stringent requirements may beapplied to assembly of sensor units which do not include a cover.

In a method according to a further embodiment of the invention, thesensor unit may include a sacrificial layer overlying the front of thesensor unit as, for example, a sacrificial layer overlying the outersurface of the cover in a sensor unit which includes a cover, or asacrificial layer overlying the imaging area of the chip in a sensorunit which does not include a cover. The assembly is fabricated with thesacrificial layer in place. The completed assembly is then subjected toan operation in which the sacrificial layer, or at least that portion ofthe sacrificial layer aligned with the imaging area of the sensor unit,is removed through hole 972 and through the one or more of the gaps 963in the support structure 952. For example, the sacrificial layer may beremoved by dissolving it, or by mechanically engaging it and peeling itaway from the sensor unit. Removal of the sacrificial layer removes anycontaminants which may have accumulated on that layer.

Other operations also may be performed through the gap or gaps. Forexample, a tool may be inserted into the gap or gaps to engage theconductors of the circuit panel and bond them to the contacts of thesensor unit. Alternatively, a wire-bonding tool may be used to providewire bonds extending between the conductors and the sensor unit throughhole 972, or through one or more of the additional apertures 974, orthrough other apertures (not shown) provided in the circuit panel forthis purpose.

It is not essential to provide post-like rear elements in order toprovide large gaps as discussed above. For example, the rear elementsmay be in the form of plates or ribs. Also, it is not essential toprovide multiple gaps; only one gap may be sufficient for someoperations.

FIG. 28 illustrates an optical unit or camera module in accordance withanother embodiment of the invention. In this embodiment, a sensor unit1120 has contacts 1142 conductively connected to terminals 1144 of acircuit panel which overlies the outer surface 1138 of the cover 1128,e.g., via solder masses 1146. Walls 1130 of the cover are preferablysloped such that the radii at edges 1132 of the walls are gradual andpreferably provide a smooth transition between a set of first contacts1134 provided on the front surface 1102 of the chip and the walls 1130.A set of conductive traces 1156, formed by processes such as thatdescribed above (FIGS. 15A through 19B) extend from the first contacts1134 along walls 1130 and onto the outer surface 1138 of cover 1128,these being conductively connected to contacts 1142. A dielectriccoating 1158, such as an epoxy or other polymeric material depositedpreferably via electrophoretic deposition, overlies the conductivetraces 1156 and is utilized as a passivation layer, e.g., solder maskwith openings exposed above the contacts 1142.

As in the example shown and described above with reference to FIG. 26,an optical unit 1150 has a set of rear elements 1162 which extendrearward from a structure supporting an optical element 1158, e.g., alens or other optical device selected from, among others, refractive ordiffractive elements, filters, reflectors and scatterers. Here again,rear surfaces 1164 of the rear element are adapted to extend through ahole 1172 in the circuit panel to abut or engage the outer surface 1138of the cover 1128 or other reference plane of the sensor unit 1120.

In the embodiments discussed above, the circuit panel has a holeextending through the panel in alignment with the imaging area of thesensor unit. Such a hole forms a transparent region in the circuitpanel. In other embodiments, the circuit panel includes a solid buttransparent region in alignment with the imaging area of the sensorunit. For example, the circuit panel may be formed from a transparentdielectric material, in which case the transparent region of the circuitpanel may be provided simply by routing the conductors of the circuitpanel so that no conductors cross the transparent region.

A packaged chip 1350 according to a further embodiment is shown in FIG.29A which includes both top conductive contacts 1308 and bottom contacts1404. Since the outer dimensions of the packaged chip 1350 are about thesame as the dimensions of the original chip 1300, the packaged chip canbe referred to as a “chip-scale” packaged chip. The packaged chip can beadvantageously incorporated into a stacked microelectronic assembly asdescribed with reference to FIG. 31 below. As shown in FIG. 29A, asemiconductor chip includes conductive features including a conductivelayer, e.g., ground plane 1316, and original contacts 1310 at a frontface 1302. A first top dielectric layer 1304, e.g. an electrophoretically-deposited coating, covers the conductive layer 1316. The conductivelayer 1316, if not already present at the front face 1302, can be formedby sputtering, plating or a combination thereof, for example, as aprelude to subsequent processing, e.g., electrophoretic deposition ofdielectric layer 1304. The electrophoretically deposited dielectriccoating 1304 serves as a dielectric level on which a first metal layer1306 is disposed above the front face 1302 of the chip. A seconddielectric layer 1305 serves as a dielectric layer on which top traces1312 and top contacts 1308 (connected through openings 1426 to the firstmetal layer are disposed. First metal layer 1306, top contacts 1308, toptraces 1312, bottom contacts 1404 overlying the rear surface 1403 andedge conductive traces 1408 along edges, 1422 are in conductivecommunication with original contacts 1310 of the chip, the conductivetraces 1306, top contacts 1308, top traces 1312, bottom contacts 1404and side conductive traces 1408, serve to redistribute the conductivecontacts from the original contacts 1310 of the chip.

FIG. 29B is a front plan view looking towards the front surface 1302showing top contacts 1308 and top traces 1312 overlying the frontsurface and side conductive traces 1408 along edges 1422 in conductivecommunication with the original contacts 1310 of the chip. FIG. 29C is arear plan view showing bottom contacts 1404 and bottom traces 1405.

Referring to FIG. 30A, in a method of fabricating the packaged chip,dielectric layers 1305 and 1402 are deposited on to top and bottomsurfaces 1403 of a microelectronic substrate such as a semiconductorwafer 1300. Boundaries between individual microelectronic elements,e.g., semiconductor chips of the wafer 1300 are indicated at 1500. Thedielectric layers 1305, 1402 can be formed by an appropriate techniquesuch as spin-coating, spray deposition, roller coating or vapordeposition, among others. The dielectric layer 1402 can beelectrophoretically deposited onto the exposed semiconductor material atthe bottom surface 1403 of the wafer by maintaining the wafer 1300 at anappropriate electric potential and immersing the wafer in anelectrophoretic deposition bath as described above (FIG. 7). Thereafter,bottom contacts 1404 are formed overlying the dielectric layer 1402. Thebottom contacts 1404 are connected to bottom conductive traces 1405. Thebottom contacts 1404 and bottom conductive traces 1405 can be formed,for example, by sputtering, plating and patterning techniques such asdescribed above (FIGS. 9-10).

Referring to FIG. 30B, a carrier substrate or carrier wafer 1410 then isattached to the bottom of the wafer 1300 such as with a removable, e.g.,peelable adhesive 1412 to form an assembly.

The original contacts 1310 of the semiconductor wafer 1300 can beexposed by forming openings through dielectric layer such as bypatterned etching, laser drilling, or other suitable process. Referringto FIG. 30C, openings 1420 aligned with the chip boundaries shown inFIG. 30B preferably can be formed by depositing a photoimageable layer1430, e.g., a photoresist, antireflective coating or other layer,patterning openings in the photoimageable layer by photolithography andthen etching the wafer 1300 from the rear face of the photoimageablelayer. The openings 1420 may extend as channels across the length andwidth of the wafer The edges 1422 of each chip 1300 which are exposed atthe walls of the openings preferably are oriented preferably at an angleof between about 10 and 60 degrees from a normal to the front face ofthe semiconductor chip. Preferably, the semiconductor element is etchedisotropically. Alternatively, the wafer 1300 can be sawn with a bladehaving a tapered profile to form the tapered openings 1420. Referring toFIG. 30D there is shown a partial perspective view facing a top surfaceillustrating the intermediate stage shown in FIG. 30C. The edges 1422 ofeach chip 1300 which are exposed at the walls of the openings aremaintained in electrical continuity. One exemplary way to accomplishthis is then the tapered openings 1420 are etched the channels separatethe walls except for the corner area 1455, 1456 & 1457. While thisexemplary embodiment shows the corner area with a mid section 1456 andsloped sections 1455 & 1457 other configurations are equally wellsuited. This corner area 1455, 1456 & 1457 maintains electricalcontinuity between the chips 1300.

After the openings are formed in the wafer, the patterned photoimageablelayer is removed from the wafer. The assembly including the wafer andcarrier wafer attached thereto is then immersed in a dielectricdeposition bath. The assembly is then held there under appropriateconditions for a sufficient time to form an electrodeposited coating onexposed exterior conductive and semiconductive surfaces of the wafer1300. As a result an edge dielectric layer 1406 (FIG. 30E) and a secondtop dielectric layer 1305 are formed such that the edge traces 1408conductively communicate with the bottom traces 1405. Alternatively,instead of electrophoretic coating, with the bottom contacts 1404covered by the adhesively attached carrier substrate 1410, the edgedielectric layer 1406 and second top dielectric layer 1305 can be formedby one or more of the above-described alternative methods, e.g.,spin-coating, spray-coating, vapor deposition, etc. After forming thedielectric layers 1406, 1305, edge traces 1408 and top contacts 1308 areformed, such as by the sputtering, plating and patterning techniquesdescribed above (FIGS. 9-10). Openings 1426 formed in the top dielectriclayer 1305, e.g., by laser drilling, patterned etching, or mechanicalprocesses, allow the top contacts 1308 to connect to the first metallayer 1306.

Referring to FIG. 31 there is shown a perspective view of a circuitpanel and a stacked layer of the packaged chip in accordance with theembodiment illustrated in FIG. 29A. Lower circuit panel 1600 has aplurality of panel contact points 1610. Packaged chip 1350 is mounted onto the lower circuit panel 1600, whereby the panel contact points 1610are in conductive contact with corresponding bottom contacts 1404 of thepackaged chip 1350. The bottom contacts 1404 may be solder balls,previously described, as well as other contact types. Additionalpackaged chips 1350 may be stacked and mounted on top of the firstpackaged chip 1350. The bottom contacts 1404 of the additional packagedchip 1350 are in conductive contact with corresponding top conductivecontacts 1308 of the initial packaged chip 1350. A top circuit panel1650 has a plurality of lower panel contact points 1660.

While FIG. 31 shows a sandwich configuration with a plurality ofpackaged chips 1350 between a top circuit panel 1650 and a lower circuitpanel 1600, the present invention is equally well suited for othersingle circuit panel configurations. One or more packaged chips 1350 maybe mounted on a lower circuit panel 1600 alone. One or more packagedchips 1350 may be mounted on a top circuit panel 1650 alone. Additionalstacks of package chips 1350 as well as individual packaged chips 1350may be mounted on the same circuit panel.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

For example, in a particular embodiment of the invention described withreference to FIGS. 29A through 30D, one or more of the dielectric layers1304, 1424 overlying the front surface 1302, the edges 1422, or the rearsurface 1403 can be formed by techniques other than electrophoreticdeposition, e.g., such as through use of spin-coating, spray depositionor vapor deposition among others. In one variation, the first topdielectric layer 1304 is formed by techniques other than electrophoreticdeposition. In such case, conductive layer 1316 at the front face 1302can be omitted.

1. A method of fabricating a microelectronic unit, the methodcomprising: providing a semiconductor chip having a front surface, arear surface remote from the front surface, at least one of conductivematerial or semiconductive material exposed at least at the frontsurface, and a plurality of first conductive contacts exposed at thefront surface, at least some of the first conductive contacts beinginsulated from the at least one of exposed conductive material orsemiconductive material; electrophoretically depositing an insulativelayer onto the at least one of exposed conductive material orsemiconductive material; forming a plurality of rear conductive traceson the rear surface of the semiconductor chip; forming a plurality offront conductive traces on the insulative layer on the front surface ofthe semiconductor chip in conductive communication with the firstconductive contacts; electrophoretically depositing a further insulativelayer onto at least a portion of the front conductive traces; forming aplurality of further conductive traces on at least part of the furtherinsulative layer on the front surface of the semiconductor chip inconductive communication with the front conductive traces; and forming aplurality of edge conductive traces that extend between the front andthe rear conductive traces, the edge conductive traces being formed atopedge surfaces that extend between the front surface and the rear surfaceof the semiconductor chip thereby conductively connecting one or more ofthe front conductive traces and the further conductive traces to therear conductive traces.
 2. The method of fabricating a microelectronicunit as recited in claim 1, wherein the semiconductor chip and at leastanother semiconductor chip are attached together at one or moreperipheral boundaries, the rear conductive traces are formed while thechips remain attached together, and the edge surfaces are defined byremoving material of one or more of the semiconductor chip and the atleast another semiconductor chip in alignment with the one or moreperipheral boundaries.
 3. The method of fabricating a microelectronicunit as recited in claim 1, wherein the front surface of thesemiconductor chip includes a conductive plane insulated from the firstconductive contacts and the insulative material is electrophoreticallydeposited over the conductive plane.
 4. The method of fabricating amicroelectronic unit as recited in claim 3, wherein the insulative layeris electrophoretically deposited over semiconductive material exposed atthe rear surface of the semiconductor chip concurrent with theinsulative layer being electrophoretically deposited over the conductiveplane.
 5. The method of fabricating a microelectronic unit as recited inclaim 1, wherein the insulative layer is electrophoretically depositedover semiconductive material exposed at the edge surfaces prior to theforming of the plurality of edge conductive traces.
 6. The method offabricating a microelectronic unit as recited in claim 2, furthercomprising severing the semiconductor chip and the at least anothersemiconductor chip along one or more dicing lanes in alignment with theone or more peripheral boundaries.
 7. The method of fabricating amicroelectronic unit as recited in claim 1, wherein the edge surfacesthat extend between the front surface and the rear surface of thesemiconductor chip are sloped at an acute angle with respect to thefront surface of the semiconductor chip.
 8. A method of fabricating aplurality of microelectronic units, the method comprising: providing aplurality of semiconductor chips formed in a substrate, each one of theplurality of semiconductor chips being attached at one or more of itsperipheral boundaries to at least another one of the plurality ofsemiconductor chips, and having a front surface, a rear surface remotefrom the front surface, at least one of conductive material orsemiconductive material exposed at least at the front surface, and aplurality of first conductive contacts exposed at the front surface, atleast some of the first conductive contacts being insulated from the atleast one of exposed conductive material or semiconductive material;electrophoretically depositing an insulative layer onto the at least oneof exposed conductive material or semiconductive material of each one ofthe plurality of semiconductor chips; and forming a respective pluralityof rear conductive traces on the rear surface of each one of theplurality of semiconductor chips; forming a respective plurality offront conductive traces on the insulative layer on the front surface ofeach one of the plurality of semiconductor chips; electrophoreticallydepositing a further insulative layer onto at least a portion of thefront conductive traces of each one of the plurality of semiconductorchips; forming a respective plurality of further conductive traces on atleast part of the further insulative layer at the front surface of eachone of the plurality of semiconductor chips in conductive communicationwith the front conductive traces of that semiconductor chip; and forminga respective plurality of edge conductive traces on each one of theplurality of semiconductor chips that extend between the respectivefront and rear conductive traces, the edge conductive traces beingformed atop edge surfaces that extend between the front surface and therear surface of each one of the plurality of semiconductor chips therebyconductively connecting one or more of the front conductive traces andthe further conductive traces of that semiconductor chip to the rearconductive traces of that semiconductor chip.
 9. The method offabricating a plurality of microelectronic units as recited in claim 8,wherein the respective rear conductive traces of each one of theplurality of semiconductor chips are formed while the plurality ofsemiconductor chips are attached together, and the edge surfaces of eachone of the plurality of semiconductor chips are defined by removingsemiconductor material in alignment with its one or more peripheralboundaries.
 10. The method of fabricating a plurality of microelectronicunits as recited in claim 9, further comprising severing the pluralityof semiconductor chips along one or more dicing lanes in alignment withthe peripheral boundaries of each one of the plurality of semiconductorchips.
 11. The method of fabricating a plurality of microelectronicunits as recited in claim 8, wherein the front surface of each one ofthe plurality of semiconductor chips includes a conductive planeinsulated from the first conductive contacts, the insulative material ofthat semiconductor chip being electrophoretically deposited over theconductive plane.
 12. The method of fabricating a plurality ofmicroelectronic units as recited in claim 11, wherein the insulativelayer of each one of the plurality of semiconductor chips iselectrophoretically deposited over semiconductive material exposed atthe rear surface of that semiconductor chip concurrent with theinsulative layer being electrophoretically deposited over the conductiveplane.
 13. The method of fabricating a plurality of microelectronicunits as recited in claim 8, wherein the insulative layer of each one ofthe plurality of semiconductor chips is electrophoretically depositedover semiconductive material exposed at the edge surfaces of thatsemiconductor chip prior to the forming of the plurality of edgeconductive traces.
 14. The method of fabricating a plurality ofmicroelectronic units as recited in claim 8, wherein the respective edgesurfaces of each one of the plurality of semiconductor chips are slopedat an acute angle with respect to the front surface of thatsemiconductor chip.
 15. A method of fabricating a plurality ofmicroelectronic units, the method comprising: providing a wafer thatincludes a plurality of semiconductor chips, each one of the pluralityof chips being attached at one or more of its peripheral boundaries toat least another one of the plurality of semiconductor chips, and havinga front surface, a rear surface remote from the front surface, at leastone of conductive material or semiconductive material exposed at leastat the front surface, and a plurality of first conductive contactsexposed at the front surface, at least some of the first conductivecontacts being insulated from the at least one of exposed conductivematerial or semiconductive material; electrophoretically depositing aninsulative layer onto the at least one of exposed conductive material orsemiconductive material of each chip of the wafer; and forming arespective plurality of rear conductive traces on the rear surface ofeach chip of the wafer; forming a respective plurality of frontconductive traces on the insulative layer on the front surface of eachchip of the wafer; electrophoretically depositing a further insulativelayer onto at least a portion of the front conductive traces of each oneof the plurality of semiconductor chips; forming a respective pluralityof further conductive traces on at least part of the further insulativelayer at the front surface of each one of the plurality of semiconductorchips in conductive communication with the front conductive traces ofthat semiconductor chip; and forming a respective plurality of edgeconductive traces on each one of the plurality of semiconductor chipsthat extend between the respective front and the rear conductive traces,the edge conductive traces being formed atop edge surfaces that extendbetween the front surface and the rear surface of each one of theplurality of semiconductor chips thereby conductively connecting one ormore of the front conductive traces and the further conductive traces ofthat semiconductor chip to the rear conductive traces of thatsemiconductor chip.
 16. The method of fabricating a plurality ofmicroelectronic units as recited in claim 15, wherein the rearconductive traces of each chip of the wafer are formed while the chipsremain attached together, and the edge surfaces of each chip of thewafer are defined by removing material at the peripheral boundaries ofeach chip.
 17. The method of fabricating a plurality of microelectronicunits as recited in claim 15, further comprising severing the chips ofthe wafer along one or more dicing lanes in alignment with theperipheral boundaries of each chip.
 18. The method of fabricating aplurality of microelectronic units as recited in claim 15, wherein thefront surfaces of each chip of the wafer includes a respectiveconductive plane insulated from the first conductive contacts thereof,the insulative material of each chip being electrophoretically depositedover its conductive plane.
 19. The method of fabricating a plurality ofmicroelectronic units as recited in claim 18, wherein the insulativelayer of each chip of the wafer is electrophoretically deposited oversemiconductive material exposed at the rear surface of each chipconcurrent with the insulative layer being electrophoretically depositedover the conductive plane.
 20. The method of fabricating a plurality ofmicroelectronic units as recited in claim 15, wherein the insulativelayer of each chip of the wafer is electrophoretically deposited oversemiconductive material exposed at the edge surfaces each chip prior tothe forming of the plurality of edge conductive traces.
 21. The methodof fabricating a plurality of microelectronic units as recited in claim15, wherein the edge surfaces of each chip of the wafer are sloped at anacute angle with respect to the front surface of that chip.